Hot pressing, or hot isostatic pressing, is used to manufacture an article, or component, by consolidating and diffusion bonding powder material together to form the article or component. Hot pressing, or hot isostatic pressing, is used to diffusion bond two or more components together to form an article and in addition hot pressing, or hot isostatic pressing is also used to manufacture an article by consolidating and diffusion bonding powder material and one or more components together to form an article.
Hot isostatic pressing of powder materials to manufacture an article involves initially forming a canister which defines the shape of the article to be manufactured. The canister is filled with powder material, the canister is evacuated to remove gases from the canister and then the canister is sealed. The sealed canister is then hot isostatically pressed to consolidate the powder material within the canister and to diffusion bond the powder material together to form the article. During the hot isostatic pressing process the particles of the powder material are initially deformed to fill the inter-particle spaces, or voids, and then the particles of the powder material are diffusion bonded together. The canister is then removed from the article by machining, by dissolving the canister in acid or by a combination of machining and dissolving in acid. The article is subsequently ultrasonically inspected to ensure that there are no defects, or flaws, in the article, e.g. voids, unbounded regions or contaminants.
U.S. Pat. No. 4,233,720 discloses a method of manufacturing an article by hot isostatic pressing and ultrasonically inspecting the article. U.S. Pat. No. 4,233,720 discloses that after the article has been manufactured by hot isostatic pressing the article is ultrasonically inspected while the article is within the canister to detect defective articles at an early stage before additional processing costs are incurred. In particular the canister is machined so that two opposite surfaces are parallel and the surfaces are ground to a suitable smoothness for ultrasonically inspecting the article within the canister. After ultrasonic inspection of the article within the canister, the canister is removed by etching in acid or by machining. The article is then machined to final shape.
There is a requirement to manufacture articles from powder material using hot pressing, or hot isostatic pressing, to net shape or near net shape, so that after the canister has been removed no, or only minimal, machining of the article is required.
A problem associated with the use of acids is that the use of acids to remove, dissolve, the canister may be precluded by environmental legislation. A further problem associated with acids is that the acids used to remove the canister may also cause damage to the article and this is of particular concern if the article is a ferritic steel or the article is a bi-metallic for corrosion resistance.
An additional problem associated with machining is that the use of machining to remove the canister may result in damage to the article because the position of the interface between the canister and the article and the positions of features of the article are not known after the hot pressing, or hot isostatic pressing, process. The position of the interface between the canister and the article after consolidation of the powder material is not known accurately because of process variations in the shrinkage of the particles of the powder material and the collapse of the canister as the inter-particle spaces, or voids, are filled by the deformation of the particles of the powder material.